Stephen that's not an ideal way to look at it and as Matt say the wheelbase increase or decreas has limited effect on how the bike steers. If you added 200mm to the wheelbase then you'd be correct but not with figures you get from adjusting the offset. You can get bigger changes from adjusting the chain...

I have a load of data I can dig out and some diagrams I used to calculate the geometry using various tyres if you're interested. My bike keeps the NSR's 35mm offset, 710mm fork length, measured from wheel spindle to top yoke face, and 87mm trail, resulting in the correct rake also when used with a 208GP front...

Changing the offset generally has the biggest effect on steering input and how quickly the bike turns. A reduced 20mm offset would 'increase' the NSR's trail by a substantial amount, from memory to around 104mm. The rake wouldn't necessarily steepen or relax and so you would have a far slower turning bike.

I spoke to these guys when designing the yokes and they have some incredibly useful info on their site and books on chassis design.

http://www.tonyfoale.com/
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NSR300R - Why did i ever have a 250...